In addition to the insurance policy, you would also need to get a Type 06 FFL. ATF is going to want proof that you are in compliance with all State and local rules for operating an ammunition manufacturing business. You also have to register under ITAR with the U.S. State Dept. and pay them around $2300 per year.
Your licensed premises can be rented as long as you have written permission from your landlord to operate a firearms business.
"Knowledge is power... For REAL!" - Jack Austin